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A non-technical explanation of port forwarding or port mapping
This article explains port forwarding or port mapping in simple language.Your home network is like a small community. Normally, the entrances (the ports) to your home network are closed to anything from the Internet that tries to get through on your home network. These entrances are kept closed by the guard (your router's firewall).
When you enable port forwarding (sometimes called port mapping), your router opens one of these entrances only to those that have the proper "key." In this case, the SlingPlayer wants to enter. To make sure that the entrance is open only to the right people and to limit their access, SlingPlayer forwards the unique Slingbox ID, along with your Slingbox password. When this forwarded information gets to your router, it opens the entrance (the port).
In other words, it is a specific connection between specific devices using a specific port.
That's port forwarding in a nutshell!
Important thing to remember: It is only necessary to set up port forwarding on the router on your home network. There is no need to make any changes on the away-from-home network you're using to watch your TV (such as the network at a hotel, at work, at a coffee shop, etc.) If you have port forwarding set up correctly on your router at home, you should be good to go.